In the motor vehicles known from the prior art, the waste heat of the engine is used for heating the supply air for the passenger space. The waste heat is transported by means of the coolant circulated in the motor cooling circuit to the air conditioning system, and there it is transferred via the heating exchanger to the air flowing into the passenger space.
Known installations with coolant-air heat exchangers pull the heating energy from the cooling circuit of an efficient combustion engine of the vehicle drive. These installations no longer reach the required level for a comfortable heating of the passenger space if the environmental temperatures are low in order to cover the total heat demand of the passenger space. Similar statements apply to installations in vehicles with hybrid drive.
When the total heat demand of the passenger space cannot be covered using the heat from the motor cooling circuit, reheating measures are required, such as electrical resistance heaters (PTC) or fuel consuming heaters. A more efficient possibility of heating the air for the passenger space is a heat pump with air as a heat source, wherein the refrigerant circuit is used both as the sole heating device and also as the reheating measure.
The air-air heat pumps known in the art which are designed for the combined chiller and heat pump mode and also for the heating mode, absorb heat from the environmental air.
Heat pump systems in which the energies can be exchanged between the refrigerant and the air frequently are unable to simultaneously dehumidify and heat the air supplied to the vehicle. This has the consequence that the air conditioning system of a motor vehicle cannot be operated using circulating air at low environmental temperatures. In the case of an operation using circulating air, the air circulates back out of the passenger space. Due to the deficient dehumidification function, the remaining air humidity as well as the water emanating from the occupants in the form of vapor would lead to fogging of the windshields.
In conventional air conditioning systems, at environmental temperatures above 20° C., once the thermal comfort has been reached, the air supplied to the passenger space is cooled to approximately 3° C. to 10° C., dehumidified in the process, and subsequently heated with low heating power to the desired supply air temperature. Thermal comfort includes, for example, a target temperature for the passenger space of approximately 20° C. to 25° C.
Glycol-air heat pumps use the coolant of the combustion engine, which usually corresponds to a water-glycol mixture, as a heat source. In the process, heat is removed from the coolant. Consequently, the combustion engine is operated for a longer time period at low temperatures, which has a negative effect on the exhaust gas emissions and on the fuel consumption. Due to the intermittent operation of the combustion engine in hybrid vehicles, a sufficiently high coolant temperature is not reached in the case of longer trips. For this reason, the start-stop operation of the combustion engine is interrupted at low environmental temperatures. The combustion engine is not switched off.
In German Pat. Appl. Pub. No. DE 10 2010 024 775 A1, a device for air conditioning vehicles is described, which can be operated both in the heating and also in the cooling mode. The device comprises a refrigerant circuit, which comprises a thermal environmental module with a condenser for the heat transfer to the environmental air, a thermal interior module with an evaporator, and a heat register for treating supply air for the passenger space, and an expansion module with an expansion valve and with a compressor for compressing the refrigerant. In addition, the device is designed with a fluid heat exchanger, which is connected in a shiftable manner to a fluid circuit that is independent of the refrigerant circuit. The components can be switched with aid of valves so that the refrigerant can admit heat in the heating mode via the connectable fluid heat exchanger or the condenser of the ambient module, or via both, which in turn can be exchanged with the inserted condensation energy via the passenger compartment module to the passenger-compartment feed air.